Cloud computing is an Internet-based computing and next stage in evolution of the internet. It has received significant attention in recent years but security issue is one of the major inhibitor in decreasing the growth of cloud computing. It essentially shifts the user data and application software to large datacenters i.e, cloud, which is remotely located, at which user does not have any control and the management of data may not be completely secure. However, this sole feature of the cloud computing introduce many security challenges which need to be resolved and understood clearly. One of the most important and leading is security issue that needs to be addressed. Data Security concerns arising because both user data and program are located in provider premises. In this study, an attempt is made to review the research in this field. The results of review are categorized on the basis of type of approach and the type of validation used to validate the approach.